Zeolites are microporous crystalline materials comprised of a crystalline network of TO4 tetrahedra which share all of their vertexes give rise to a three-dimensional structure containing channels and/or cavities of molecular dimensions. They are of varying compositions, and T generally represents atoms in a formal +3 or +4 oxidation state, such as, for example Si, Ge, Ti, Al, B, Ga, . . . . If any of the T atoms has an oxidation state of under +4, the crystalline network formed has negative charges which are offset by means of the presence of organic or inorganic cations in the channels and cavities. In these channels and cavities, organic molecules and H2O can also be housed, therefore being possible to state the chemical composition of zeolites using the following empirical formula:x (M1/nXO2):y YO2:z R:w H2Owhere M represents one or more +n organic or inorganic cations; X represents one or more trivalent elements; Y represents one or more tetravalent elements, generally Si; and R represents one or more organic compounds. Although by means of post-synthesis treatments, the nature of M, X, Y and R and the values of x, y, z, and w can be varied, the chemical composition of a zeolite (as when synthesized or following the calcination thereof) possesses a characteristic range of each zeolite and of the method for obtaining the same.
On the other hand, the crystalline structure of each zeolite, with a specific network of channels and cavities, gives rise to a characteristic X-ray diffraction pattern. Therefore, zeolites differ from one another due to the range of their chemical composition plus their X-ray diffraction pattern. Both of these characteristics (crystalline structure and chemical composition) also determine the physicochemical properties of each zeolite and the possible application thereof in different industrial processes.
In U.S. Pat. No. 4,439,409, a description is provided of a material referred to as PSH-3 and the method for synthesizing the same by using hexamethyleneimine as the structure-directing agent. Subsequent thereto, other materials having certain similarities also obtained by hexamethyleneimine, such as MCM-22 (U.S. Pat. No. 4,954,325), MCM-49 (U.S. Pat. No. 5,236,575) and MCM-56 (U.S. Pat. No. 5,362,697) have been described.